Life is a series of building blocks. We learn to crawl, then walk and eventually run. Joe Lally, an Iowa State University nutrient management specialist, likens that progression to the succession of steps in manure containment and management in Iowa's feedlots, with the latest step being a move beyond the environmental benefits to those of cost savings and sustainability.

Lally, along with USDA Agri-cultural Research Service (ARS) researchers Tom Moorman and Jeremy Singer of the National Laboratory for Agriculture and the Environment in Ames, IA, have worked with several Iowa producers over the past couple of years to improve their use and efficiency of feedlot manure in crop production. One of the things they've learned is that timed application of feedlot effluent on a cover crop of cereal rye not only captures feedlot manure's nitrogen (N) to provide another supply of harvested forage in the spring but also retains N in the soil for use by the summer crop (Tables 1 and 2).

“The use of a cover crop appears to be a useful method of capturing manure N and recycling it into silage,” the researchers said in a progress report released this summer. “Based on these preliminary data, producers may be able to increase annual silage production (both corn and cover crop) by including the cover crop in their crop-production system. The rye cover crop will also protect the soil from erosion and help maintain soil organic matter.”

Joe Lally puts it another way: “We could potentially take $100/acre off the cost of production. We don't get many opportunities like that in life to ratchet down costs. Usually it's a penny here and a penny there.” He says it's a practice that could be applicable west to Nebraska, east to Ohio and south to northeast Kansas and northwest Missouri.

New structures

Surface runoff ponds are a relatively new feature of the Iowa feeding landscape, brought on by new Environmental Protection Agency requirements on concentrated animal feeding operations (CAFO). Most Iowa feedlots of more than 1,000 head have constructed such containment facilities and irrigate the liquids onto nearby cropland, generally using center-pivot irrigation systems, Lally says.

The collection and storage facilities utilize pickets to strain off liquids from the solids. The liquids are irrigated onto cropland; the leftovers are field spread.

“Our first serious effluent applications were in 2007,” Lally says of his Iowa CAFO work. “That's when we learned how to manage the water, how the basins filled and didn't fill.”

Once the facilities and their management were in hand, the next logical step was to maximize the value of the manure.

“The reason for cover crops is for nutrient retention, minimizing soil erosion and adding organic matter to the soil,” says Singer, a research agronomist. “So, typically the cover crop is sprayed with herbicide in the spring and tilled under with the cash crop to follow.”

But one of the traditional problems with production of cover crops is getting them started in the fall. They're generally planted late in the year after the summer crop has been harvested and soil moisture is lagging. So, the cover crop goes in the ground and just sits there.

“With center pivots, it's a whole new ballgame,” Lally says. “If you put the water down as soon as you put down the cover crop, germination is no longer an issue and it provides a stronger stand going into the winter.” Plus, the head start offers great potential for a crop in the spring.

A unique project

While considerable research has been conducted over the years on cover crops, this project was unique, Lally points out.

“We really wanted to use cover crops to capture existing nutrients and keep them there for further use in the next crop,” he says. “Our goal is to capture the N that we're putting down with these systems. We don't want it to leach out; we want to capture it in the root zone until we get a growing crop of corn there to use it.”

So, working with an Iowa feedlot, a 7,000-head-capacity operation on which the ARS researchers had conducted effluent analysis and soil tests, rye was drilled on 141 acres following harvest of corn silage. Half of those acres were center-pivot irrigated with effluent.

The corn silage harvest for the 2008 crop year — 32 tons/acre — had been completed on Sept.17, and the rye planted two days later. The center pivot was operated on Sept. 22, Oct.19, Nov. 19 and Nov. 24 to empty the feedlot's runoff detention basin. Altogether, the applications of effluent delivered 100-150 lbs. of N/acre.

On Nov. 25, soil samples, root and shoot growth measurements were taken at four locations. The sampling process was repeated on May 14, 2009, except that an area of the field under the center pivot without a cover crop was sampled, the researchers report.

By May, the cover crop shoots had accumulated 200 lbs./acre of N, which was mostly captured by harvesting the cover crop.

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